1. Field of the Invention:
This invention relates to a method and apparatus for increasing the storage capacity of a water pool for storing spent nuclear fuel rods.
2. Description of the Prior Art:
Spent nuclear fuel rods from nuclear reactors are normally stored in deep water pools in storage racks for sufficient periods to permit the residual reactivity of the nuclear fuel to dissipate or until the spent fuel rods are withdrawn from the pool for transportation to a spent fuel recovery installation. Typical fuel rods are individual cylinders of about 1/2 inch diameter and about 8 feet long which are confined within a fuel rod assembly while they are in a nuclear reactor and subsequently while they are stored in a deep water storage pool. It is a normal practice to provide spaces between the spent fuel rod assemblies to preclude any unintended temperature increase within the water storage pool. When a water storage pool has its alternate storage rack positions filled with spent fuel rod assemblies there is no space remaining within the deep water pool for additional assemblies of spent nuclear fuel rods.
It has been proposed to withdraw the spent fuel rods from the assembly in which they have a normal spacing and to compact the spent fuel rods in a canister in which the fuel rods are compacted in tighter spacing. The more compact spent nuclear fuel rods do not present the same tendency for temperature increase and can be stored in adjacent and contiguous spaces in a storage rack, thereby increasing the storage capacity of an existing storage rack threefold. See copending U.S. patent application Ser. No. 291,230 filed on Aug. 10, 1981 by W. J. Wachter.
A serious consequence of increasing the storage capacity of existing storage racks in deep water pools is that the floor (usually concrete) of such deep water pools may have its loading capacity exceeded by such increased storage. It is essential to maintain the spent fuel rods under at least 10 feet of water at all times, including those times when the spent fuel rods are being transferred from their fuel rod assemblies into a compacted fuel rod canister. Accordingly, typical water storage pools are about 45 feet deep and contain metal storage racks at their base. The fuel container storage racks have a height which corresponds approximately to the length of the nuclear fuel rod assemblies, typically 12 feet or 15 feet. The anticipated floor loading, thus, is the weight of the 45 feet deep water pool and the contained storage rack and spent fuel rod containers. The increased load of fuel rods resulting from compaction and consolidation of the fuel rods into containers utilizing all of the spaces in the storage rack will significantly increase the bearing load applied to the floor of the deep water pool. The cost savings achieved from the threefold increase in storage capacity for spent nuclear fuel rods cannot be permitted to jeopardize the structural integrity of the water pool floor.